Reduced noise level brush chipper

ABSTRACT

A quite brush chipper having a bladed cutter head and a flywheel has the moment of the flywheel increased so that the combined kinetic energy of the cutter head and the flywheel at 1,550 RPM is at least equal to the combined kinetic energy of these elements in prior chippers at 3,000 RPM, so that the quiet chipper can be driven at 1,200 - 1,600 RPM for reducing the noise level while providing sufficient stored kinetic energy for effective intermittent chipping.

United States Patent 1 Gunnarsson May 6,1975

[ REDUCED NOISE LEVEL BRUSH CHIPPER [75] Inventor: Arne N. Gunnarsson,Pomona,

Calif.

[73] Assignee: FMC Corporation, San Jose, Calif.

[22] Filed: Nov. 21, 1973 [21] Appl. No.: 418,006

[52] US. Cl 241/221; 241/292.1 [51] Int. Cl. B02c l/08 [58] Field ofSearch 241/221, 222, 220, 198 R,

241/189 R, 186 R, 186.2, 285 R, 291, 292.1

[56] References Cited UNITED STATES PATENTS 2,345,779 4/1944 Wagner241/189 X 2,679,873 6/1954 Hill 241/186 X 3,270,968 9/1966 Hess et al241/221 3,771,733 ll/1973 Hadley et a1 241/186 R Primary Examin'erRoyLake Assistant Examiner-DeWalden W. Jones Attorney, Agent, or FirmC. E.Tripp [57] ABSTRACT A quite brush chipper having a bladed cutter headand a flywheel has the moment of the flywheel increased so that thecombined kinetic energy of the cutter head and the flywheel at 1,550 RPMis at least equal to the combined kinetic energy of these elements inprior chippers at 3,000 RPM, so that the quiet chipper can be driven at1,200 1,600 RPM for reducing the noise level while providing sufficientstored kinetic energy for effective intermittent chipping.

2 Claims, 5 Drawing Figures PATENTEE HAY 5 I975 SHEET 10F 3 PATENTEBHAY61975 SHEET 2 BF 3 T'IE'I IEI REDUCED NOISE LEVEL BRUSH (IHIPPER FIELDOF THE INVENTION This invention relates to wood chippers for branches,brush, etc. and more particularly to the reduction in the noise level ofthese devices.

DESCRIPTION OF PRlOR ART A brush chipper cutter head of the type towhich this invention relates is exemplified by the US. Pat. No. to Hall3,195,592, July 20, 1965. Such brush chippers include a housing whichmounts a rotary, generally cylindrical cutter head having a plurality ofcutter blades that run very close to a fixed bed knife. Although notshown in the Hall patent, these chippers customarily include a chipdisposal chute and the cutter head shaft mounts a pulley that is drivenby a source of power, usually a gasoline engine. The other side of thecutter head shaft mounts a flywheel to increase the kinetic energy ofthe rotating assembly and usually includes a blower which directs air toa disposal chute for assistance in moving chips out the chute and into areceptacle.

When properly adjusted, the sharpened blades on the cutting head orrotor just clear the bed knife, the clearance being a maximum of aboutone-sixteenth of an inch. Typical prior chippers of this type, having acutting head of about 1 l to 13 inches in diameter, must be operated ata minimum speed of 2,200 rpm and often up to a speed as high as 3,000rpm. These speeds are required with chippers of this type in order toprovide adequate chipping for medium or heavy branches without stallingthe power source, usually an internal combustion engine. The engine isfitted with an automatic governor which is set to maintain the engine ata nominal operating speed, both when the machine is at standby inbetween chipping operation and during the actual chipping operation,although the engine does slow down somewhat under the chipping load.This governed speed, which may be as high as 3,000 RPM (for example)will be referred to herein as stand-by speed or operation.

Experience shows that chippers of this type run at standby, that is whenthey are not being used for cutting or chipping, for about 88 to 95percent of the total running time of the machine. During this idlingtime, the cutter knives, which run close to the bed knife, act as asiren and create an objectionable noise. Such noise has a level highenough that prolonged exposure to the noise at distances in the order offeet or so, can damage the human ear. it is also known that the damageis accumulated, meaning that an operator who is exposed to the noiseover a substantial period of time can suffer permanent auditory damage,as compared with minor and usually transitory damage sustained by thosewho are only subjected to the noise occasionally. For example, priorchippers of the type described may, when at stand-by, have a noise levelat about 20 feet in the front or rear of the machine that is equal to orexceeds 100 dB measured on the A scale by a standard, commercial typenoise level meter. This noise level, which is within the range of noiseproduces by a pneumatic peening hammer, not only occurs during therelatively small fraction of the time during which the machine ischipping but is generated during the major portion of the running timeof the machine, and has been considered objectionable psychologically tothose close to the machine. Also, this noise level is unacceptable underpresent government regulations, such as the Noise Level Standards of theFederal Office of Safety and Health Administration (OSHA).

The chipper of the present invention operates at a reduced noise levelwithout impairing chipping efficiency. Previous chippers, operating atan objectionably high noise level, have been designed to rotate thecutter head at speeds ranging from a minimum of 2,200 rpm to 3,000 rpm.Chippers operating at these speeds produce the objectionably high noiselevels previously described. it was conceived that operation of achipper at lower speeds might reduce the noise level. Experiments showedthis to be the case. For example, when running a chipper at about 1,550rpm, the noise level at stand'by is reduced from that of priorconventional or standard chippers operating at a stand-by speed of 3,000rpm by about 9 10 dB on scale A of the noise level meter. Specifically,the noise level of the slower machine at the noisiest position, namelyabout 20 feet from the rear of the machine, is reduced from over 100dB-A to about dB-A, a decrease of 9 10 dB.

it was found that it is not possible to operate the prior chipper atspeeds low enough to reduce the noise to a satisfactory level, becausethe engine would stall under load and the kinetic energy imparted to thechips by the action of the cutting head was not high enough tosatisfactorily throw the chips out of the disposal chute and up into thereceptacle or truck bed. Also, the standard machine, when operated atreduced speed, would not satisfactorily be self feeding on brush or thelike during cutting. in order to permit operation of the chipper at astand-by speed low enough to provide satisfactorily low noise levelswithout sacrificing actual cutting effectiveness, chip disposal and selffeeding, under the present invention, it was found that if the mass ofthe rotating parts were increased so that the kinetic energy of therotating mass at the lower speed stand-by operation equaled or exceededthe kinetic energy of the rotating mass at the prior high speeds, thenthe advantages in noise reduction provided by a lower standby speedcould be attained without sacrificing cutting and chip disposaleffectiveness. More specifically, it was found that the cutting headcould remain the same as before but that increasing the moment of theflywheel by a factor of more than two would result in satisfactoryoverall operation. With this concept, the stored kinetic energy of thecutting head and flywheel asssembly of the improved, quieter machine atan operational speed of about l,550 rpm (for example) somewhat exceededthe stored kinetic energy in the prior machine operated at 3,000 rpm(for example). This modification reduced the noise level and providedadequate performance. It was further found that with improved design ofthe present invention the frequency or pitch of the noise generated bythe machine at lower speeds was reduced by one octave. This reduction infrequency of the stand-by noise of the chipper augmented the effects ofreduction in the basic noise level because it has been found thatpsychologically, the noise generated at a lower frequency,characteristic of the chipper of the present invention, is less annoyingthan that generated at the higher frequency, characteristic of priorchippers of the type described.

Thus, as a result of the present invention, only is the stand-by soundlevel of the chipper reduced without sacrificing the effectiveness ofoperation during cutting, but the frequency of the sound level idling islowered and these factors decrease the psychological noise effects ofthe machine.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of a brushchipper embodying the present invention, with parts broken away.

FIG. 2 is a section taken on line 2 2 of FIG. 1.

FIG. 3 is a plan view of the brush chipper with the parts broken away.

FIG. 4 is an enlarged fragmentary section showing a cutting head and bedknife assembly.

FIG. 5 shows noise level comparison curves between a standard chipperand the quiet chipper of the present invention operating at stand-by.

GENERAL DESCRIPTION OF THE Cl-IIPPER Referring to FIGS. 1, 2 and 3, thechipper of the present invention includes a stand that supports a cutterhead housing 12. A cutter head or rotor R is rotatably supported in thehousing 12 and carries four blades 14 which run close to a fixed bedknife 16 for chipping. A feed chute 17 projects rearwardly from thecutter housing 12 and a discharge chute 18 projects forwardly from thehousing for conveying chips removed by the cutter head from logs orbranches L to an associated truck or container. The mechanism justdescribed is mounted on a base or frame partially indicated at 19, itbeing conventional in this art to construct the frame as a wheeledchassis which not only supports the chipper under description butsupports an internal combustion engine or other prime mover for drivingthe cutter head rotor R.

Rotor Construction A typical cutter head R comprises a drum-like rotorindicated generally at 30 (FIG. 4) and which is provided with fourinclined slots 32 for receiving the cutter blades 14. Each cutter bladeis formed with a serrated surface 34 which matches a complementarysurface formed on a wall of the associated slot 32. Each blade isclamped by a clamp plate 36 and a clamp bolt 38 which passes through aslot (not shown) in each blade 14 to accommodate adjustment for bladewear. As best seen in FIG. 4, the bed knife 16, which is shown as beingof hexagonal construction, is clamped in a groove formed by the edge ofa wall of the cutter housing 12 and the edge of a frame element 40 bymeans of one or more clamp bar 42 and a clamp bolt 44. It is to beunderstood that the details of the cutter blade mounting and of the bedknife construction are not criticai to the present invention, but in allcases the blades 14 run very close to the cutting edge of the bed knife16 and hence provide a narrow air escape gap indicated generally at g inFIG. 4. This gap, which is one-sixteenth of an inch wide or less, causesthe cutter head R to act as a siren, particularly during the 88 95%operating time that represents stand-by operation. Reduction in thelevel of the noise produced by this siren effect represents a principalconsideration of the present invention. Cutter Head Mounting and FlyWheel The cutter head or rotor R is mounted on a sturdy shaft 50 and theshaft is supported by the housing 12 in a manner of which is notcritical to the present invention. As seen in FIG. 2, one end portion ofthe cutter head shaft 50 is mounted in a side plate 52 of the cutterhousing 12 by means of a combined radial and thrust anti-frictionbearing 54 mounted in a sieeve 56 projecting from the side plate 52 andlocated by spacers. The other end portion of the cutter head shaft 50 ismounted in the opposite side plate 58 of the cutter head housing in asleeve 60 that also supports the shaft in an anti-friction bearing. Itis understood that the details of the bearing mount for the cutter shaft50 are not critical to the invention and suitable constructions are wellknown in the art.

Referring to FIG. 2, an inner flywheel housing section 62 is secured asby screws (not shown) to the free end of the side plate sleeve 56,previously described. A large flywheel 64 has a hub 66 that is formedwith a key way and the hub fits over the reduced diameter, projectingend 68 of the shaft 50, which end also mounts a flywheel key 70. Theflywheel 64 and the impeller 72 of a blower are secured to the endportion 68 of the shaft by a bolt and clamp washer assembly illustratedgenerally at 74, it being understood that the details of the manner ofsecuring the flywheel and blower impeller to the shaft are not criticalto this invention and are well known in the chipper art. The blowerhousing 20, previously mentioned, is detachably secured to the flywheelhousing section 62 by means of a flange 76.

In order to assist in ejecting chips from the cutting area of thedelivery chute the centrifugal blower impeller 72 has radial impellervanes 82 and a central inlet throat 84. The blower housing 20,previously mentioned, has an air inlet tube 86 that makes a running fitwith the inlet throat 84 of the blower by means of an annular flexiblering 87. An air filter 88 covers the air opening provided by the inlettube 86. Some installations incorporate a brake assembly, illustratedgenerally at 90, and associated with the flywheel 64 for quickly.bringing the unit to a stop when necessary. The details of the brakeassembly (if present) are not critical to the present invention.

In order to drive the cutter head shaft 50 from an internal combustionengine, or other prime mover, a mul tiple V-belt pulley 92 is connectedto and keyed to the end of the shaft on the right side of the machine.The pulley 92 is driven by V-belts from an engine pulley not shown inthe drawings, it being understood that this means of driving chippercutter heads is known in the art.

Ouieting the Chipper Once it had been ascertained that the stand-bynoise level of the chipper could be reduced to an acceptable standard bylowering the speed of the chipper cutter head to a minimum of 1,200 RPM(below which chip ejection becomes a problem) or to a maximum of l,550to 1,600 RPM (above which the noise level is not sufficiently reduced),it became necessary to devise a means for providing effective cutting bythe chipper over this lower speed range. Of course, the obviousexpedient would be simply to change the ratio of the engine and chipperdrive pulleys to cause the chipper to operate at a lower speed. However,this expedient is inoperative because it was found that during actualcutting, the chipper speed would drop below the acceptable lower limitsfor effective cutting and chip removal. Consideration of the problemindicated the possibility that if the kinetic energy of the rotatingportions of the chipper, when operating at speeds such as 1,550 RPM forexample, could be maintained equal to or somewhat greater than thekinetic energy of a standard chipper when running at speeds such as3,000 RPM for example, the stored kinetic energy of the rotating partsofslower speed chipper might be sufficient to perform the intermittenttype of chipping operation usually carried out by these machines, andwithout causing the speed of the cutter head to drop below an acceptableminimum speed of 1,200 RPM.

To give a specific example, a typical cutter head for one of thesechippers will be about 1 1 inches in diameter and 12 inches long, with aweight of about 470' pounds. The fly wheel of the above exemplarymachine is about 21 inches in diameter, about 2.5 inches wide and weighsabout 210 pounds. The kinetic energy of the rotating mass including theflywheel and cutter head of this typical prior assembly is about 198,000ft. lbs. at 3,000 RPM. In a machine embodying the present invention, andusing the cutter head described above, it was decided to increase thekinetic energy of the rotating mass by increasing the moment of theflywheel. This was accomplished by leaving the flywheel width at 2.5inches, and increasing the flywheel diameter from 21 inches to about 32inches, giving a flywheel weight of about 532 pounds. As mentioned, thecutter head weight remains at 470 pounds. This gives a kinetic energy of211,000 ft. lbs. at an RPM of 1,550, which speed, as previouslymentioned, produces an acceptably low noise level.

Tests of the quieter machine, having a stored kinetic energy of 211,000ft. lbs. at 1,550 RPM, showed that during the intermittent cuttingoperation to which these machines are normally subjected, the speed ofthe cutter head did not drop below an acceptable value for effectivecutting and chip disposal.

FIG. 5 is a composite of four noise level curves A, B, C and D givingthe comparison of noise levels of what is termed the standard chipperrunning at 3,000 RPM, the specifications of which have been mentionedbriefly, as compared with the noise level of what has been termed aquiet chipper running at 1,550 RPM. Measurements were taken using aGeneral Radio Sound Level Meter, type 1,565B calibrated by a GeneralRadio Sound Level Calibrator, type 1,562, manu factured by the GeneralRadio Company of West Concord, Mass, U.S.A., the principles of which aredescribed in the Handbook of Noise Measurement, 6th Edition, by Petersonand Gross, published by the General Radio Company.

Test readings were taken on scale A of the meter which scale compensatesfor the psychological effect of pitch or frequency of noise on the humanear. The readings were initially plotted on a polar chart (not shown)that is, they were taken at various positions circumferentially aroundthe machine and at three distances, namely a 7 meter radius, a 50 footradius and a 100 foot radius. The test curves of FIG. 5 are selectedfrom the aforesaid set of circumferential readings of both chippers inthat they represent readings taken at the left and right hand sides ofthe chipper (curves A and B) and readings taken at the rear and front ofthe chipper, (curves C and D).

Examination of the test curves of FIG. 5 show that the quiet chipper ofthe present invention (solid lines) had a noise level at stand-by ofabout 9 dB-A less than that of the standard chipper at stand-by (dottedlines) throughout substantially the entire test. A study of the testfigures obtained from which the curves of FIG. 5 were plotted shows thatthe noise level drops off sharply as the cutter rpm is reduced andremains relatively flat in the rpm range of 1,200 to 1,600, which rangeis selected as the operating range of the quiet chipper of the presentinvention during cutting.

Further examination of the four curves of FIG. 5 shows that the highestnoise levels are at the rear of the machine, curve C. At about 20 feetfrom the chipper, the noise level of the standard chipper (dotted line)was about 102 dB-A and the noise level at 40 feet about 97 dB-A.

The noise level of the quiet chipper (solid line curve C) at about 20feet from the rear of the machine, dropped from 102 dB-A for thestandard chipper to 93 dB-A for the quiet chipper. Since a noise leveldrop of 3 dB-A represents halving the power level of the noise, theaforesaid total drop of about 9 dB provided by the quiet chipperdecreases the power level of the noise of the quiet chipper toone-eighth of that of the standard chipper.

Curve C also shows that at a distance of about 40 feet, the noise levelof the standard chipper was 97 dB-A whereas that of the quiet chipperdropped to 87 dB-A. Curves A,B and D of FIG. 5 show correlated results,but all of these noise levels are somewhat less than those of curve C.

As mentioned, the aforesaid brief description of curve C of FIG. 5 havebeen directed to conditions at the very loudest zones of operation ofthe chipper. In order to give some comparison of the intensity level ofthe noise generated by these chipper operations with the soundsgenerated under more familiar conditions, the aforesaid Handbook of HandNoise Measurement, page 5 and the Elements of Physics by Shortley andWilliams, Prentice and Hall, Inglewood, N..l., U.S.A. (second edition)page 407 give the following examples of the intensity levels of commonlyexperienced sounds.

Thus under the present invention, not only has the noise level of thequiet chipper been substantially reduced but since its speed is slower,the frequency of the noise is lower than that from the standard chipper.

Sound level studies have shown that the apparent loudness that weattribute to a sound varies, not only with the sound pressure orintensity but also with the frequency or pitch of the sound.sychologically, it is known that sounds or noises at relatively lowfrequencies are not as noticeable or objectionable as noise phenomena asare sounds of the same intensity but having higher frequencies. In thequiet chipper of the present invention, with a 4 blade cutter headconstruction described, the frequency of the idling noise (stand-by)generated by standard chipper running at 3,000 rpm would be about 200Hz, whereas that of the quiet chipper running between 1,200 and 1,600rpm will be about to 100 Hz. Psychologically, the apparent loudness ofnoises of equal sound pressures but at different frequency ranges willnot be the same. The apparent loudness of the lower frequency noise willbe less than that of the higher frequency noise. This effect, which is acharacteristic of the chipper of the present invention, representanother aspect of the reduction in the objectionable characteristics ofthe noise emanating from the chipper, particularly during stand-byoperation, which represents about 80 95% of the total operating time.

In the specific example described in detail herein, the cutter head was11 inches in diameter and 12 inches long. Actually commercial machinesof this type may have cutter heads of l l 16 inches diameter and 12 16inches length. However, the principles of applying the teachings of thepresent invention to machines employing cutter heads of different sizesremain the same. The moment of the flywheel will be increased tomaintain cutting effectiveness and adequate chip disposal when operatingthe machine at speeds in the range of about 1,200 1,600 rpm.

Although the best mode contemplated for carrying out the presentinvention has been herein shown and described, it will be apparent thatmodification and variation may be made without departing from what isregarded to be the subject matter of the invention.

What I claim is:

1. In a brush chipper of the type comprising a housing having a bedknife therein, a shaft driven cutter head having a diameter of about 1 l13 inches and a length of about 12 inches, said head mounting cutterblades that project only a short distance from the head, feed anddisposal chutes on said housing, means for driving said cutter head; anda flywheel on said cutter head shaft; the improvement wherein saidcutter head and said flywheel have a combined kinetic energy of about200,000 ft. lb. at a rotational speed of about 1,550 rpm,

said means for driving said cutter head shaft driving the I shaft at astandby speed within the range of about 1,200 1,600 rpm for causing thenoise level generated at the rear of the chipper as the cutter headblades pass the bed knife to be within a range of about dB-A at feet toabout 93 dB-A at 20 feet while providing sufficient stored kineticenergy for effective intermittent chipping.

2. The brush chipper of claim 1, wherein said flywheel is a flat steeldisc about 2.5 inches thick and about 30 to 32 inches in diameter.

1. In a brush chipper of the type comprising a housing having a bedknife therein, a shaft driven cutter head having a diameter of about11 - 13 inches and a length of about 12 inches, said head mountingcutter blades that project only a short distance from the head, feed anddisposal chutes on said housing, means for driving said cutter head; anda flywheel on said cutter head shaft; the improvement wherein saidcutter head and said flywheel have a combined kinetic energy of about200,000 ft. lb. at a rotational speed of about 1,550 rpm, said means fordriving said cutter head shaft driving the shaft at a standby speedwithin the range of about 1,200 - 1,600 rpm for causing the noise levelgenerated at the rear of the chipper as the cutter head blades pass thebed knife to be within a range of about 80 dB-A at 100 feet to about 93dB-A at 20 feet while providing sufficient stored kinetic energy foreffective intermittent chipping.
 2. The brush chipper of claim 1,wherein said flywheel is a flat steel disc about 2.5 inches thick andabout 30 to 32 inches in diameter.